W32.Zori.B

SUMMARY

W32.Zori.B is a virus that prepends itself to .exe files and spreads through network shares. The virus deletes files from all disks nine days after the original infection.

Protection

• Virus Definitions (LiveUpdate™ Weekly) March 31, 2005
• Virus Definitions (Intelligent Updater) March 31, 2005

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 0 - 49
• Number of Sites: 0 - 2
• Geographical Distribution: Low
• Threat Containment: Easy
• Removal: Moderate

Damage

• Damage Level: High
• Deletes Files: Deletes files after nine days.
• Modifies Files: Prepends its code to .exe files found.
• Degrades Performance: Propogation may degrade performance.
• Compromises Security Settings: Attempts to delete security related registry keys and disable security related processes.

Distribution

• Distribution Level: Low
• Ports: TCP port 1879
• Shared Drives: May also spread by copying itself over Windows file shares.

TECHNICAL DETAILS

When the W32.Zori.B is executed, it performs the following actions:

1. Creates and opens a file named andylau.bmp, displaying the following image:
   
   
   
   
2. Creates copies of itself as the following files:
   
   
   • C:windows empssshost.exe
   • %Windir%svchost.exe
     
     Note: %Windir% is a variable that refers to the Windows installation folder. By default, this is C:Windows or C:Winnt.
     
     
3. Adds the value:
   
   "Microsoft" = "%Windir%svchost.exe"
   
   to the registry subkey:
   
   HKEY_LOCAL_MACHINESOFTWAREMicroSoftWindowsCurrentVersionRun
   
   so that W32.Zori.B runs every time Windows starts.
   
   
4. Adds the value:
   
   "(Default)" = "%Windir%svchost.exe "%1" %*"
   
   to the registry subkey:
   
   HKEY_LOCAL_MACHINESOFTWAREClassesexefileshellopencommand
   
   so that W32.Zori.B runs every time Windows starts.
   
   
5. Adds the value:
   
   "Version" = "0x3E9"
   
   to the virus created registry key:
   
   HKEY_LOCAL_MACHINESOFTWAREmysoft
   
   as an infection marker:
   
   
6. Opens a back door on TCP port 1879 that connects to the youda2000.vicp.net domain and listens for commands from an attacker.
   
   
7. Attempts to end the following processes and then prevent them from running when Windows starts:
   
   
   • pfw.exe
   • kvfw.exe
   • KAVPFW.EXE
   • iamapp.exe
   • nmain.exe
   • freepp.EXE
   • freekav.EXE
   • freesys.EXE
   • Iparmor.exe
   • trojan_hunter.exe
   • Rfw.exe
   • rav
   • taskmgr.exe
     
     
8. Attempts to delete the following values:
   
   "SKYNET Personal FireWall"
   "iDuba Personal FireWall"
   "iamapp"
   "rfw"
   "popproxy"
   "RavMon"
   "RavTimer"
   
   from the registry key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   which may prevent some programs from running when Windows starts.
   
   
9. Searches the hard disks for .exe files and infects them by prepending its code to them. Infected files increase by 623,116 bytes.
   
   
10. May spread by copying itself over Windows file shares.

Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

• Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates.
• If a blended threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
• Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services (for example, all Windows-based computers should have the current Service Pack installed.). Additionally, please apply any security updates that are mentioned in this writeup, in trusted Security Bulletins, or on vendor Web sites.
• Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate infected computers quickly to prevent further compromising your organization. Perform a forensic analysis and restore the computers using trusted media.
• Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.

REMOVAL

The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

1. Disable System Restore (Windows Me/XP)
2. Restart the computer in Safe mode or VGA mode.
3. Reversing the changes made to the registry.
4. Reinstall your Symantec AntiVirus Product
5. Update the virus definitions.
6. Run a full system scan and delete all the files detected as W32.Zori.B.
   

For specific details on each of these steps, read the following instructions.

1. To disable System Restore (Windows Me/XP)
If you are running Windows Me or Windows XP, we recommend that you temporarily turn off System Restore. Windows Me/XP uses this feature, which is enabled by default, to restore the files on your computer in case they become damaged. If a virus, worm, or Trojan infects a computer, System Restore may back up the virus, worm, or Trojan on the computer.

Windows prevents outside programs, including antivirus programs, from modifying System Restore. Therefore, antivirus programs or tools cannot remove threats in the System Restore folder. As a result, System Restore has the potential of restoring an infected file on your computer, even after you have cleaned the infected files from all the other locations.

Also, a virus scan may detect a threat in the System Restore folder even though you have removed the threat.

For instructions on how to turn off System Restore, read your Windows documentation, or one of the following articles:

• "How to disable or enable Windows Me System Restore"
• "How to turn off or turn on Windows XP System Restore"

Note: When you are completely finished with the removal procedure and are satisfied that the threat has been removed, re-enable System Restore by following the instructions in the aforementioned documents.

For additional information, and an alternative to disabling Windows Me System Restore, see the Microsoft Knowledge Base article, "Antivirus Tools Cannot Clean Infected Files in the _Restore Folder," Article ID: Q263455.

2. To restart the computer in Safe mode or VGA mode
Shut down the computer and turn off the power. Wait for at least 30 seconds, and then restart the computer in Safe mode or VGA mode.

• For Windows 95, 98, Me, 2000, or XP users, restart the computer in Safe mode. For instructions, read the document: How to start the computer in Safe Mode.
• For Windows NT 4 users, restart the computer in VGA mode.

3. Reversing the changes that were made to the registry
Because the worm infects .exe files, first make a copy of the Registry Editor as a file with the .com extension, and then run that file.

1. Do one of the following, depending on the version of Windows you are running:
   • Windows 95/98 users:
     1. Click Start.
     2. Point to Programs.
     3. Click the MS-DOS Prompt. (A DOS window opens at the C:Windows prompt.) Proceed with step B of this section.
        
        
   • Windows Me users:
     1. Click Start.
     2. Point to Programs.
     3. Point to Accessories.
     4. Click the MS-DOS Prompt. (A DOS window opens at the C:Windows prompt.) Proceed with step B of this section.
        
        
   • Windows NT/2000 users:
     1. Click Start > Run.
     2. Type command, and then press Enter. (A DOS window opens.)
     3. Type cd winnt, and then press Enter.
     4. Proceed with step B of this section.
        
        
   • Windows XP users:
     1. Click Start > Run.
     2. Type command, and then press Enter. (A DOS window opens.)
     3. Type the following:
        
        cd
        cd windows
        
        Press Enter after typing each one.
        
        
     4. Proceed with step B of this section.
        
        
2. Type copy regedit.exe regedit.com
   
   and then press Enter.
   
   
3. Type start regedit.com
   
   and then press Enter. (The Registry Editor opens in front of the DOS window.)
   
   After you finish editing the registry, exit the Registry Editor, and then exit the DOS window as well.
   
   
4. Before continuing, Symantec strongly recommends that you back up the registry before making any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify the specified subkeys only. For instructions, read the document, "How to make a backup of the Windows registry."
   
5. Navigate to the subkey:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   
6. In the right pane, delete the value:
   
   "Microsoft" = "%Windir%svchost.exe"
   
   
7. Navigate to the subkey:
   
   HKEY_LOCAL_MACHINESOFTWAREClassesexefileshellopencommand
   
   
8. In the right pane, edit the value:
   
   "(Default)" = "%Windir%svchost.exe "%1" %*"
   
   erase the "Windir%Svchost.exe", so when you are finished it should read:
   
   "(Default)" = "%1" %*
   
9. Navigate to and delete the subkey:
   
   HKEY_LOCAL_MACHINESOFTWAREmysoft"Version" = 0x3E9
   
   
10. Exit the Registry Editor.

5. To reinstall your Symantec antivirus program
As this virus attempts to remove the files and registry subkeys that your Symantec antivirus program uses, you may need to reinstall the program. If your Symantec antivirus program is not working properly, uninstall, and then reinstall it.

6. To update the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:

• Running LiveUpdate, which is the easiest way to obtain virus definitions: These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate).
• Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted daily. You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater).
  
  The Intelligent Updater virus definitions are available: Read "How to update virus definition files using the Intelligent Updater" for detailed instructions.

7. To scan for and delete the infected files

1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
   • For Norton AntiVirus consumer products: Read the document, "How to configure Norton AntiVirus to scan all files."
   • For Symantec AntiVirus Enterprise products: Read the document, "How to verify that a Symantec Corporate antivirus product is set to scan all files."
2. Run a full system scan.
3. If any files are detected as infected with W32.Zori.B, click Delete.